This invention relates to a solenoid actuated valve.
U.S. Pat. No. 4,811,754 issued Mar. 14, 1989, the disclosure of which is hereby incorporated by reference herein, describes a solenoid actuated valve for controlling flow of aqueous rinse liquid to a vacuum toilet and is particularly designed for use in an aircraft toilet system in which the rinse liquid is potable water. The valve comprises an armature that is fitted for sliding movement within a tube through which the rinse water itself also flows. Movement of the armature under control of a solenoid that is located outside the tube controls movement of a closure member into and out of contact with a valve seat. This valve operates without need for an external linkage connecting the moveable closure member to a source of mechanical power, or for seals preventing leakage around such a linkage.
In a valve of the kind shown in U.S. Pat. No. 4,811,754, the armature must be free to move axially within the solenoid bore, and the gap between the armature and the solenoid bore must be minimized in order to avoid flux leakage.
In a practical implementation of the valve shown in U.S. Pat. No. 4,811,754, the armature was made of nickel-plated stainless steel. This material was satisfactory when the valve was new because the nickel plating providing a good bearing surface. However, the plating was subject to wear and/or oxidation, so that the quality of the bearing surface deteriorated. This resulted in the armature movement being impeded, so that the valve became unreliable. For example, the valve might remain open when it should have closed, and it might remain closed when it should open.
Various efforts have been made to solve the problems of wear and oxidation. Chromium plating the armature was unsuccessful because the chromium plating also was subject to wear and/or oxidation. A plating of nickel impregnated with PTFE was subject to oxidation, and poor adhesion between the stainless steel armature and the plating resulted in worse wear performance than the simple nickel plating.